The literal translation would be "ξέχασέ το". However this is not very common in Greek.
Better phrases would be "Ούτε να το σκέφτεσαι" (= don't even think about it), or "σε καμία περίπτωση" (=no way, no chance).
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.